Nondiabetic (ND) subjects who carry a mutation for the HNF-4-alpha gene, the MODY1 gene, have impairment of glucose-induced insulin secretion. We wished to ascertain the effects of the nonglucose secretagogue arginine (A) on plasma concentrations of insulin, C-peptide and glucagon, on insulin secretion rate (ISR), and on glucose potentiation of A-stimulated insulin secretion in 14 ND subjects of the RW MODY1 pedigree: 7 gene positive (+), 7 negative (-), and 4 mildly diabetic (DM+).